The invention concerns a metal filter mat for use in reversible-flow filter devices, according to the preamble to patent claim 1.
The pressure filters commonly used in engineering generally contain a changeable filter mat, which is mounted on the base of the filter or on parts of the filter housing. In order to keep the filter mat from getting clogged or to remove filter cakes completely from the filter after the filter process, so-called reverse rinsing is used, i.e., a rinse process with a gas or liquid in the opposite direction from the main flow. The reverse rinse is supposed to extend the life of the filter mat, and when a suction filter is used, it should help meet strict purity specifications and remove the filter cake with no residue. However, the reverse rinse process is time-consuming and does not always produce the success desired. Particularly high demands are made on the strainer for residue-free removal when the sequence of lots involves a change of product, and with sensitive materials, for example in the chemical-pharmaceutical field, there is a danger of cross-contamination.
The known filter mats are multilayer and consist of wire gauze whose mesh size, starting from the mesh width necessary for the respective filter process, becomes increasingly coarse in the flow direction. Due to the multilayer design of the conventional filter mat, a certain static strength is achieved during the pressure filter process.
But with very firmly adhered filter cakes or stubborn residues in the filter mat, during the reverse rinse, some parts are discarded or separated in the reverse rinse direction. This makes not only the mat body unusable. Especially with suction filters, removal elements, for example stirring and peeling arms, are arranged at very short distances over the surface of the filter. If the filter were discarded, the filter cake would have to be peeled off by hand, in order to prevent damage to the removal elements. If the lots of product are sensitive, i.e., must be processed sterile, this ruins the whole lot. The attendant loses are substantial. In order to circumvent the above problem in practice, the filter cake, especially in conventional pressure filters, is removed mostly by the effect of centrifugal forces or with the aid of flyweight motors.
The task of this invention is to make an improvement in filter mats so that better stability is guaranteed, especially during the reverse rinse and, if necessary, the drying process and so that the filter devices can be operated more effectively during production or processing.